Means for fabricating piezoelectric crystal units



1947- A; L. w. WILLIAMS 2,414,574

MEANS FOR FABRICATING PIEZOELECTRIC CRYSTAL UNITS Filed Oct. 16, 1942 Fllll v r W FIEZ I INVENTOR. ALFM'D L. H WILLIAMS Patented Jan. 21, 194? MEANS FOR FABRICATING PIEZOELECTRIC CRYSTAL Alfred L. W. Williams, assignor to The Brush Development Company,

a corporation of Ohio Cleveland, Ohio,

UNITS Cleveland Heights, Ohio,

Application October 16, 1942, Serial No. 462,236

3 Claims. (01. ac -tor This invention relates to means for fabricating piezoelectric crystal units.

As pointed out in the United States patent to Sawyer et al., No. 2,112,636, the fabrication of extremely thin piezoelectric crystal sections from Rochelle salt or the like, is best accomplished in four steps, 1. e., producing a relatively thick slab of crystalline material from mother crystaL.

sawing the slab into a plurality of plates, subjecting the plates to a milling operation and caused to adhere. The first and second steps of the process may satisfactorily be accomplished through utilization of the apparatus disclosed in the United States patent to Sawyer, No. 1,764,088. Because of the extreme frangibility and sensitivity to heat of Rochelle salt sections, however, the employment of conventional milling cutters, intended for use on metals, results in excessive spoilage and consequent waste. 1

The -primary object of this invention, therefore, is to produce apparatus for subjecting a section of frangible piezoelectric material to a milling operation without causing breakage or causing spoilage because of heat.

Another object is to produce apparatus of the type described through the employment of which dimensionally accurate piezoelectric crystal sections having smooth, parallel faces may be fabricated.

The foregoing objects and other objects ancil lary thereto are accomplished, in a preferred embodiment of the invention, by causing a crystal section to so move horizontally in a plane parallel to and slightly below the axis about which a horizontally extending milling cutter rotates that the cutter makes line contact with the upper face of the crystal and removes therefrom a surface layer having predetermined thickness. A roughing and a finishing cutter may disposed, sequentially, adjacent to the path of movement of the crystal section, if desired.

For the purpose of preventing heat from spoiling the crystal section, it is supported upona massive table of material having high heat cn= 'ductivity, such as metal, which table may be caused to reciprocate in a horizontal plane or 2 to rotate about a vertical axis to bring the section in contact with the cutter or cutters.

Inasmuch as his inexpedient to employ mechanical devices for holding the section to the moving table while the said section is being subjected to the milling operation, means are provided whereby atmospheric pressure is utilized automatically, so to speak, for that purpose. In order that atmospheric pressure shall be applied to the crystal section during the time that it is being milled, the table is provided with a plurality of small channels that extend between the upper and lower faces thereof and means, such as a vacuum pump, are provided for exhausting air from the channels immediately below the section. and closely adjacent thereto only while the section is in the neighborhood of a cutter. The movement of the table into and out of the work zone controls the application of the vacuum, in the preferred embodiment, thus facilitating the loading of the table with sections and their removal therefrom subsequent to the milling operation.

' The novel features considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself; however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing, wherein:

Figure l is a plan view, partly broken away, showing the essential elements of a milling cutter constructed according to the invention, and

Figure 2 is a view, partly in elevation and partly in vertical cross section along a line substantially corresponding to the line iii-H in Figlire 1.

In both figures of the drawing, identical elements are similarly designated. it is to be understood, also, that many conventional portions of the apparatus, such as the prime mover, the vacuum pump, the means for adjusting the position of the cutter vertically with respect to the crystal sections, etc., have been omitted inas-' much as they form no part of the present invention.

Referring now to the drawing, the preferred embodiment of the invention includes a circular work-supporting table l, keyed to a vertical spindle 3 which receives relatively slow rotary motion from a prime mover (not shown). Suitable bearings of conventional type (not shown) are provided for the spindle and the table, if

desired. may be supported at its periphery upon a fixed circular track or conventional tim also not illustrated because it forms no part of the present invention. The table is provided with a large number of small channels 5, that termipate in openings in the upper and lower faces thereof. A rotary milling cutter l is mounted to extend inwardly over the upper face otthe table from the periphery in the direction of the spindle, the axis of rotation of the cutter being parallel to the plane of rotation of the upper surface of the table. Means (not shown) are provided for raising an lowering the-cutter and cut taken from a crystal section 8 as it is carried beneath the cutter by the rotating table.

To provide means for guiding and urging a crystal section beneath the cutter, the upper surface of the table carries a masking disc 8 having a plurality of angularly spaced crystal-receiving windows it formed therein.

A threaded extension '53 of the rotary spindle extends through a central aperture in the masking disc and a nut 65, having a wide laterally extending flange ii, is threaded on the spindle and so holds the disc rigidly, yet removably, in fixed position that it revolves with the table.

The windows ii in the masking disc expose only the openings of the channels extending through the table directly beneath them; the re maining channels are blocked oil by the imperia rate portions of the disc.

Dimensionaliy, the windows are slightly longer and. somewhat wider than the particular crystal section which is to be subjected to the milling operation, thus facilitating loading and unloading. Should it be desired to operate upon crystal sections that previously have been provided with electrodes and an electrode lead It, each window may be provided with a lateral extension is to accommodate the lead and to keep it out of the path of the cutter.

The disc, preferably, is fabricated from a material such as a laminated thermo-setting plastic that is fairly hard yet is reasonably flexible; its thickness is somewhat less than that to which the crystal section is to be finally milled.

A wide variety of masks may be provided for accommodating crystal sections of various shapes and thicknesses, thus rendering the cutter extremely versatile. Also, it is to be understood that the entire table may be provided with air channels to further extend the range of usefulness of the apparatus to include crystal sections wider than those shown in the drawing. I

In order that atmospheric pressure may be utilized, automatically, for holding a crystal sec tion in place upon the table during the milling operation, the open end of an intake pipe 2i leading to an exhaust pump (not shown) is positioned fixedly beneath the table directly below the milling cutter and the gap between the lower surface of the'moving table and the edge of the open end is made air-tight through utilization of packing means such as a resilient gasket 23 disposed around the pipe. Alternatively, the end of the intake pipe may connect with an exhaust chamber (not shown) that ofiers either a smaller or a larger effective opening to the table than the pipe, depending upon the dimensions of the crystal sections that the apparatus is intended to mill.

When setting the device into operation, the first step is to place a masking disc, having windows of the proper dimensions, upon the table and acres i a to lock it firmly in position thereon by turnin down the lock nut. Thereafter, the milling cutter.

which rotates in a direction to oppose the movement of a crystal section past it, is set into motion,

5 the exhaust pump or fan (not shown) is started.

and the table is caused to slowly rotate in the direction of the arrow in Figure l.' A crystal section is placed in one of the windows as the table moves pest station A and the milling cutter is lowered and locked in position to remove a layer of the requisite thickness from the upper surface at the section. g

es the table moves toward the "wor position beneath the cutting tool the channels through the table below the section are exposed to the intake of the vacuum pump and atmospheric pressure acts upon the surface of the section to hold it firmly in place until the cutting operation is completed. As the crystal section moves beyond the work position, leaving the cutter, the op nings oi the table channels below the section clear the intake opening and the pressure is released, automatically, thus permitting the operator to remove the finished section and to deposit another one in the window. 'No specific directions can m given with respect to the depth of material that may safely be removed iroma section during a single pass nor can the angular velocity of the table or the revolutions per minute oi the cutter be exactly determined in advance. Those iactors, obviously,

depend upon the size and thickness of the section being milled and upon the efilcacy oi the metal table in removing heat generated during the milling operation.

To some extent, at least, the table and crystal section are cooled by air that leaks past the crys= tal and the mask and a separate air-blast for cooling purposes has not been found necessary. An additional exhaust system (not shown) may be provided for carrying away and for recovering the crystalline material removed by the cutter and an air-blast or suction means (not shown) may also be utilized for cleaning the crystal and 45 the table during the cutting operation.

The invention also includes the positioning of more than one milling cutter in the path of movement of the crystal sections, for the purpose of removing the surface of a section in a succession to of operations. In that modification, the vacuum may or may not be broken between successive cutters. Obviously, a second cutter could be mounted at a location indicated, for example, by the letter B in figure 1, and the intake of the 55 vacuum pump, or a chamber connected thereto 1 could extend to cover-the table-channels at the second location as well as those included in the arc of movement of a crystal section between the two locations. Such modification of the inven- 50 tion is so obvious that no necessity is seen for illustration thereof.

in the event that it is desired to finish both v sides of a section before it isnnally removed from the device, a second cutter 'l and exhaust to pipe 23 may be added to the apparatus exemplifled by Figure 1'. The additional cutter, for example, might be mounted diametrically opposite to the cutter shown and another operator, located at a position indicated by the letter- C, 7 could remove each section as it leaves the first work zone and replace it in the window with the unmilled side uppermost for milling by the second cutter. This additional modification of the invention is believed to be also so obvious as 76 to need no illustration.

The inventor is fully aware of the fact that work-holding means of the vacuum type have been employed hitherto in connection with machine tools and he is familiar with the prior art exemplified, for example, by the United States patent to Fellow at al., No. 1,119,111. Insofar as he is aware, however, the semi-automatic utilization of such vacuum means in connection with the milling of frangible piezoelectric crystal sections is novel with him and it is believed to be an important contribution to the art.

'Although several specific embodiments of the invention have been disclosed and described herein, it is to be understood that they are merely illustrative and that other modifications may be made without departing from the spirit and scope of the invention as claims.

What is claimed is:

In a machine which includes a work tool, the combination of movable means including a table having a plurality of interior passageways that terminate in openings in a surface thereof for supporting an object and for moving it into engagement with said tool, means for exhausting the air between the object and the supporting means through said interior passageways to establish a holding vacuum therebetween during the time period of engagement of the tool with defined in the appended the object, and masking means removably secured against said table for preventing motion of said masking means with respect to said table and for substantially preventing air from being drawn through passageways adjacent to those covered by the object, said masking means establishing an abutment for helping to hold said object from sliding in a plane parallel to the plane of the face of said table as said work tool operates on said object.

2. The device as defined in claim characterized in this; that said interior passageways terminate in openings extending circumferentially around said table, and said masking means includes a plurality of windows each located ad-- jacent some of said openings and each for receiving one of said objects whereby the openings located under each window exhaust the air beways terminate in openings extending circumferentially around said table whereby a plurality of said openings will always register with the windows in said substitute masks despite the difl'erent size or shape of the windows therein.

ALFRED L. w. WILLIAMS. 

